The present applicant, in order to reduce the weight of the seat structure, proposes a variety of seat structures using three-dimensionally knitted fabrics and two-dimensional fabrics as the base net for the cushion frame and the back frame. Patent Documents 1-3 describe configurations in which certain cushion characteristics are applied by stretching the base net via a torsion bar, and compared to the conventional so-called “placement structure” in which a urethane material of a certain thickness is installed on top of a cushion pan, weight is reduced while posture supportability, body pressure dispersibility, and vibration absorbing characteristics, etc. are improved.